1. Field of the Invention
This application is based on Japanese Patent Application No. 2007-088748, the content of which is incorporated herein by reference.
The present invention relates to a combined cycle power generating plant.
2. Description of Related Art
In recent years, thermal power plants that use liquefied natural gas and the like as a fuel have come to be widely used. A combined cycle power generating plant that is provided with a gas turbine plant and a steam turbine plant is widely used as such a thermal power plant.
In the combined cycle power generating plant described above, first, a gas turbine drives a generator to generate power. Simultaneously, in a heat recovery steam generator, the heat (exhaust heat) that has been discharged from the gas turbine generates steam by evaporating condensed water that has been supplied from a condenser. Steam that is thereby generated is supplied to the steam turbine and the steam turbine is thereby driven. A generator is driven by the steam turbine to generate power. Note that combined cycle power generating plants include those that are constructed such that separate shafts are provided to the gas turbine and the steam turbine, and each drives a separate generator, and those that are constructed such that a gas turbine, a steam turbine, and a generator are linked by a single shaft, and the single generator is driven.
It is known that the thermal efficiency (power generation efficiency) of the power generating plant that is used in the gas turbine described above is improved by increasing the temperature of the combustion gas at the inlet of the gas turbine. However, when the temperature of the combustion gas at the inlet is high, there is a concern that damage and melting of the high-temperature section of the gas turbine (for example, the combustor, the gas turbine stator blades, and the gas turbine rotor blades and the like) may occur due to the heat of the combustion gas. Thus, technology has been proposed in which the high-temperature section of the gas turbine is cooled to prevent damage and melting due to heat (Japanese Patent No. 3068925 and Japanese Unexamined Patent Application, First Publication No. 2000-248962).
The above two publications disclose a technology in which steam is used as a cooling medium that cools the high-temperature section of the gas turbine.
In the case in which steam is used as the cooling medium, when the pipes and the like (the cooling steam system) that supply steam become cool, a portion of the steam is condensed, and a drainage of water drops and the like is generated. The water drops are directed along with the steam to the high-temperature section of the gas turbine, and there is a concern that the water drops will be brought into contact with the high-temperature section of the gas turbine. The high-temperature section of the gas turbine with which water drops have come into contact is locally cooled, and thus there is a concern that the durability thereof will be reduced due to thermal stress.
Here, examples of a state in which the cooling steam system has cooled include the time during which the gas turbine plant is being started up and the time during which the gas turbine plant is being stopped.
In order to solve the problems described above, a method is known in which a gas turbine plant is warmed by channeling steam for a predetermined time to a cooling steam system before the gas turbine plant is started up (this is referred to as “warming”), and the formation of water drops inside the steam system is thereby prevented.
However, in the method in which the steam system is warmed simply by channeling steam in sequence from the upstream side of the cooling steam system, there are problems in that the warming takes time, and thus the start-up of the gas turbine plant (i.e., combined cycle power generating plant) takes time.